The Late Paleoproterozoic Lapland–Mid-Russia–South Baltia orogen surrounds the Karelian craton as a wide arc, separating it from Volgo-Uralia and Sarmatia. The orogen extends for more than 3000 km; its width in the northern and central segments is 400–700 km and increases to 1000 km in the southwest.
The Lapland sector of the orogen is characterized by specific spatial distribution of tectonic belts composed of low-grade metavolcanic-metasedimentary rocks and granulite-gneiss complexes. The former are localized along the orogen boundaries; in turn, the axial zone is mainly formed by alternation of low-angle tectonic sheets varying in thickness from a few to 20–25 km. The sheets are composed of Paleoproterozoic granulite-gneiss complexes and Archean granite-greenstone and amphibolite-gneiss assemblages. The geological history of the orogen is subdivided into four stages. (1) The Early Paleoproterozoic magmatism (2.53–2.41 Ga, locally up to 2.32 Ga) corresponds to the initial stage in evolution of the superplume, which induced rifting of the Archean continent. This stage includes: the early volcanism (ca. 2.5 Ga), the layered peridotite-gabbronorite intrusions (2.53–2.42 Ga), bimodal volcanism (2.45–2.42 Ga), emplacement of the minor mafic intrusions that were later transformed into drusites (2.46–2.43 Ga), formation of the Pyrshin-Kolvitsa gabbro-anorthosite complex (2.51–2.42 Ga), and intrusions of charnockites and K-rich granites (2.50–2.43 Ga) and granitoids (2.50–2.41, up to 2.37–2.36 Ga). The Pyrshin-Kolvitsa gabbro-anorthosites underwent granulite-facies metamorphism along with mafic protolith of the Lapland and Kolvitsa-Umba granulite complexes. The domain of initial magmatism in the Kola-Karelia region is a NW-trending band, 1000–1100 km in extent and 300–450 km in width. The area of manifestation of various modes of Early Paleoproterozoic magmatic activity can be regarded as a large igneous province. (2) The initial magmatism was followed by a long-term (2.3–2.1 Ga) stage of quiescent tectonics. Sedimentation in the Karelian Province initially occurred in the vast lacustrine-alluvial plain, then in the nearshore marine and continental evaporite basin, and by the end of this stage in a shallow-water marine basin characterized by deposition of evaporite carbonate and sulfate sediments and growth of numerous stromatolite reefs. The accumulation of salt has been documented by deep drilling in the Onega depression. The basement and sedimentary sequence were cut through by a NW-trending dike swarm almost synchronously with sedimentation. In the southwestern part of the basin within Karelia, separate lava fields were formed, whereas in Kola Peninsula, volcanic activity was much more intense, and sedimentation had been suppressed. (3) The resumption of tectonic activity by the onset of the Late Paleoproterozoic is recorded in a vigorous pulse of magmatic activity (2.11–1.92, locally up to 1.88 Ga), which was somewhat similar to the Early Paleoproterozoic initial magmatism. It developed within the same NW-trending band as the Early Paleoproterozoic initial magmatism. As in the previous case, the area of the Late Paleoproterozoic magmatism corresponds to the definition of a large igneous province. It involves: (i) mafic volcanic rocks inherent to continental and oceanic rifts (including the Jormua ophiolite complex) in combination with a bimodal rhyolite-picrite association close in geochemistry to ocean-island basalt and subvolcanic minor gabbro and wehrlite intrusive bodies (2.11–1.92 Ga); (ii) volcanic-sedimentary and mafic-ultramafic subvolcanic complexes of the Onega depression (ca. 1.98 Ga); (iii) Kimozero kimberlites (ca. 2.0–1.8 Ga); (iv) Jaurijok complex of gabbro-anorthosite intrusions (from 2.0–1.95 to 1.88 Ga); and (v) alkali intrusions (from 1.97–1.95 to 1.88 Ga) and granitoid plutons (ca. 1.95 Ga). All gabbro-anorthosite bodies of the Jaurijok complex are localized at the base of nappe-thrust ensemble of the Lapland granulite belt, i.e., in exactly the same position as the Early Paleoproterozoic Pyrshin-Kolvitsa complex. Appearance of the suprasubduction magmatism in volcanic-sedimentary belts almost at the same time (1.93–1.86 Ga) marked a change from the extensional regime to compression in the Paleoproterozoic history of the East European craton for the first time in Paleoproterozoic history. (4) The subsequent stage, with predominance of collisional and postcollisional processes (1.87–1.70 Ga), resulted in eventual formation of the intracontinental collisional orogen.
In the history of the Lapland and Kolvitsa-Umba granulite-gneiss belts, an emplacement of the Pyrshin-Kolvitsa gabbro-anorthosite and granulite-facies metamorphism M0 were broadly coeval with Early Paleoproterozoic plume-influenced rifting of the Archean supercontinent ca. 2.51–2.44 Ga. This period was followed by deposition of volcaniclastic protoliths of the lower part of the Lapland granulite complex, which probably occurred within the intracratonic extensional basin. The next episode of plume-related extension, which induced emplacement of the Jaurijok gabbro-anorthosite bodies, lasted from 1.97 to 1.89 Ga. High-grade metamorphism M1 (ca. 1.95 Ga) and then pervasive granulite-facies metamorphic events M2 (1.95–1.91 Ga) and M3 (1.91–1.89 Ga) followed at the end of this episode. At the same time, in the area of low-grade volcanic-sedimentary belts, opening and subsequent closure of local intracontinental oceans occurred due to rapid subduction and/or obduction of the oceanic lithosphere.
The Mid-Russia sector (basement of the East European platform—territory of the Moscow syneclise) is the central part of the southern branch of the Lapland– Mid-Russia–South Baltia orogen surrounding the Karelian craton in the south. The Totma belt extends along the northern boundary, separating the Paleoproterozoic orogen from the Karelian craton, while the southern boundary, which separates the Paleoproterozoic orogen from the Volgo-Uralia continent and Sarmatia, is marked by the Aprelevka and Kazhim belts. The Kashino, Zubtsovsk-Diakonovo, Dmitrov-Galich, Moscow, Lezhsk-Grivino, and Oparino granulite-gneiss thrust-nappe belts are crucial in the upper-crustal structure of the Mid-Russia sector. They are combined with Archean or Paleoproterozoic gneiss-amphibolite-migmatite complexes in the Bologoevo, Tver, Bukalovo, and Ivanovo-Sharya belts. As a whole, the Mid-Russia sector of the Paleoproterozoic collisional orogen is a giant synform, 300–350 km wide and 1400 km long. The synform is composed of tectonic sheets, 6–8 km thick, alternating in vertical and lateral directions and formed by the Paleoproterozoic and Archean granulite-gneiss and migmatite-amphibole-gneiss complexes. It is bordered by tectonic sheets of volcanic-sedimentary belts conformably plunging southeast.
The South Baltia sector of the orogen (basement of the East European platform—Southern Baltic region and Belarus) is composed of a series of arcuate (crescentic) belts consisting of metamorphic rocks ranging in grade from greenschist to epidote-amphibolite or from high amphibolite to granulite facies. The sector, which extends for 1200 km toward the northeast, is up to 800 km wide. The arcuate outlines of belts in the South Baltia sector are convex to the east. The internal structural elements of belts and their boundaries are generally characterized by westward centroclinal plunges. In the west, the South Baltia sector is cut off by the Transeuropean suture (Teisseyre-Tornquist Line), which separates it from the Hercynides of East Europe. The eastern part of the South Baltia Sector contains the Staraya Russa–South Finland granulite-gneiss belt, Ilmenozero migmatite-amphibolite-gneiss belt, and Vitebsk and Toropets granulite-gneiss allochthons. The northern segment of the South Baltia sector dominates the area and is composed of alternating arcuate (crescentic) belts: the Belarus-Baltic granulite-gneiss belt, Latvia–East Lithuania migmatite-amphibolite-gneiss belt, and West Lithuania granulite-gneiss belt at the western boundary of the East European craton. In the southern segment of the South Baltia sector, the sequence of the belt from west to east includes the Central Belarus migmatite-amphibolite-gneiss belt and the southern part of the Vitebsk granulite-gneiss allochthon. The South Baltia sector is, to a greater extent, similar in composition and structure to the other sectors of the Lapland–Mid-Russia–South Baltia intracontinental orogen. This implies that granulite-gneiss belts of the South Baltia sector most likely are underlain by Archean or Early Paleoproterozoic crust.
